The devices are known by the trade name Stingray. The report says they raise concerns for privacy advocates because law enforcement officials won't say how often they use them, how the data is used, or whether they get a warrant before using it.

Law enforcement officials declined interview requests and redacted references to the Stingray in public records requested by the Gannett Wisconsin Media Investigative Team. But documents show the devices have been used for years by both the Wisconsin Department of Justice and the Milwaukee Police Department.